The present invention relates generally to sediment control barrier systems and relates more particularly to filtration barriers for waterborne silt and to methods and apparatus for installing the silt filtration barriers, of which the following is a specification, reference being had to the accompanying drawing, forming a part hereof.
Sediment control barrier systems have a variety of uses and a wide range of industrial applications. They include: protection of surface soils from surface water erosion, the trapping of sediment, and run-off water filtration for improving water quality, and preventing waterborne silts and solids from entering channeled streams and drainage control systems.
A wide variety of materials and structures are used in sediment control barriers systems and in geo-barrier systems in general. Since terminology is somewhat non-standardized, the following terms are defined herein. The term ‘geo- fabric’ refers to a geo-textile, geo-membrane or a geo-grid structure, or to a combination of thereof. The term ‘geo-textile’ refers to a woven, non-woven, or knitted, biodegradable-resistant fabric that is sufficiently porous as to allow movement of air and water. Geo-textiles are typically load-bearing, synthetic fabrics used as a filter to prevent the passing of fine grained material such as silt or clay. The term ‘geo-grid’ refers to biodegradable-resistant material manufactured into an open, lattice like sheet configuration. Geo-grids are typically made of plastic and used as a reinforcing structure. The term ‘geo-membrane’ refers to essentially impermeable polymeric sheets. Geo-membranes are typically used as hydraulic barriers in liner and cover systems.
Sediment control barriers include silt fences constructed of filtering fabrics, support posts and wire fences. Silt fences are, typically, single vertical barriers made from a geo-fabric supported in upright position by posts and support mesh. More particularly, typical silt fences are temporary sediment barriers made of woven synthetic filtration fabric supported by steel or wooden posts. Silt fences prevent sediments carried by un-channeled or sheet flow of storm or rainwater from leaving a ground site and either entering natural drainage channels or entering waste and storm drain systems. The barriers slow the runoff sheet flow and frequently create a ponding of water upstream of the silt fence. The reduction in water velocity causes the larger entrained soil particles to settle to the ground surface upstream of the silt fence. A silt fence constructed of permeable geo-textile sheets creates a filtration barrier that filters non-colloidal, suspended silt particles as the low velocity or ponded water passes through the silt fence to form an effluent stream. The filtered silt particles are shed from the vertical fabric barrier surface of the standard silt fence and accumulate at its base. The size of the barrier openings determine the size of the particles filtered. The size, shape and number of the openings, as well as the height of the ponded water, determine the flow rate of the filtered effluent stream.
Un-channeled surface water that is deposited upon ground having a sloped surface flows by gravity directed flow along paths determined by the contour of the ground surface. Typically, a silt fence is installed along a path spanning the sloped ground surface or along a path spanning beneath such a slope. The installation path is selected such that it is transverse to the water flow path and impedes the flow. But, the installation path is not necessarily orthogonal to the direction of runoff water flow at each point along the path. Since sheet flow run-off is stored upstream of a silt fence, the slope grade and the slope length determine the hydraulic load experienced by the silt fence. A maximum recommended slope length upstream of an installed silt fence is determined based on the mechanical strength of the silt fence assembly, the flow rate through the barrier and the volume of water per unit slope area per unit time expected to be deposited upon the slope.
A standard silt fence assembly consists of a woven geo-textile sheet stapled to a series of long wooden stakes. The typical length of the stakes is 48 inches and the stakes are typically made of a hardwood. The stakes are installed at intervals of from 4 to 6 feet and are driven into the ground along a selected path typically over a contour of the surface transverse to the path of ground water run- fence before the lateral forces of hydraulic load become too much for the system to bear and ultimately cause the silt fence system to collapse.
What is needed then is a silt fence system that can be installed using a shallower embedment depth of the posts while retaining or improving the stability of the silt fence.
Additionally, what is needed is a silt fence assembly which is capable of carrying a greater hydraulic load than the vertical post of the standard silt fence assembly.
An additional need is a silt fence assembly that increases percentage of geo-textile surface area used for filtering while maintaining effective silt shedding characteristics.